Question

I am experiencing an interesting issue when I am trying to load some data in .txt format from the same domain using XMLHttpRequest.
I am trying to load the data, parse it and then store it in localStorage

var xmlhttp;
// code for IE7+, Firefox, Chrome, Opera, Safari
if (window.XMLHttpRequest){
    xmlhttp=new XMLHttpRequest();
}else{
    // code for IE6, IE5
    xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}

var temp;
xmlhttp.onreadystatechange=function(){
    if (xmlhttp.readyState==4 && xmlhttp.status==200){
        temp = xmlhttp.responseText;

    }else{
        alert("readyState: " + xmlhttp.readyState + "status: " + xmlhttp.status);
    }
}
xmlhttp.open("GET","data/somedata.txt", false);
xmlhttp.send();

This code only works if I clean the history and cache; however, on second click of the same link, I would received “Readystate: 4, status 0” for some reason.

Does this has anything to do with localStorage?

if (!localStorage.somedata || localStorage.somedata.count(':') !== somedata.count(':')) {
  localStorage.somedata = temp;
}
window.somedata = JSON.parse(localStorage.somedata);

Answer 1

There are two causes of status code of zero.

1. Making calls from the file protocol.
2. The page is refreshing/navigating away as the request is being made.

In your case I would assume it is #2. If you are using a button or a link to make the Ajax call, make sure to cancel the click action with either preventDefault or return false.